Study On Equivalent Influence Of Key Parameters On Natural Gas-CO₂-Air Premixed Combustion

With the rapid development of the industry of internal-combustion engine and the rapid increase in the number of vehicle ownership,problems of energy shortage and environmental pollution are becoming increasingly serious.To solve the problems the promising ways are application of alternative fuels.Due to its abundant reserves,clean and other advantages,thus,Natural gas can be efficiently used to mitigate shortage of petroleum energy and air pollution.Meanwhile,the technology of applying natural gas into engine is relatively mature,and natural gas equivalent combustion coupled with the technology of EGR（exhaust gas recirculation）can significantly improve the natural gas engine emissions,especially can largely reduce NOx emissions.However,application EGR（diluent gas）always decreases in flame propagation speed and chemical reaction rate of mixed gas,which will results in prolonging the duration of combustion,and reducing thermal efficiency of the engine.In order to solve the problem of decreasing the burning rate of natural gas mixture,improvement the combustion characteristics of natural gas engines and enrichment the theoretical knowledge of natural gas combustion.In this paper,based on the experimental bench of the constant volume combustion chamber,the key parameters of the natural gas-CO₂-air premixed combustion equivalent impact was systematically investigated by using schlieren photography and spherical expansion flame method.In this paper,the equivalent effects of initial temperature,initial pressure,equivalence ratio,and dilution rate on the premixed combustion characteristics of natural gas mixture were analyzed.two research and analysis routes are included by this paper.The first analysis route is to reveal the equal effect of initial temperature and CO₂ dilution rate on flame propagation velocity,laminar combustion rate,flame development period,combustion duration,and NOx emission of natural gas premixed combustion.The second analysis route is to reveal the equal effect of initial temperature and initial pressure on flame propagation velocity,laminar combustion rate,flame development period,combustion duration,and NO_x emission of natural gas premixed combustion.The following several conclusions are obtained:The flame propagation speed and laminar burning rate both increased with the increase of the initial temperature,however,both of them decreased with the increase of initial pressure and CO₂ dilution rate.To some extent,coupling effect between dilution rate and initial temperature has equal effect on natural gas premixed combustion.At the condition of the similar stretched flame propagation velocity,although unstretched flame propagation velocity,flame development period and combustion duration are almost the same,there is a large difference in laminar burning rate.With a small dilution rate,the unstretched flame propagation velocity and laminar burning rate are more affected by the dilution rate than the initial temperature.At initial pressure of 0.3 MPa and equivalence ratioΦof 1.0,initial temperature differenceΔTu of 50 K and dilution rate differenceΔDR of 2%have a certain amount of influence on natural gas premixed combustion,and the effects of the two factors are very similar.In addition,the coupling influence between the initial temperature and the initial pressure has the same effect on the flame propagation velocity and the laminar combustion rate of natural gas premixed combustion.At the condition of the similar flame propagation velocity,which the difference in flame stability and the difference of the state density before and after the combustion lead to the difference of the combustion state parameters and the results of the emission products in the non laminar combustion process.